Hello barnpotato,
It must be a scary time for your daughter and a confusing one for you! First off, make sure you go to a therapist that works a lot with anxiety and uses cognitive behavioral therapy to treat it. In the meantime, read a lot about anxiety and make sure you tell your daughter that while it is very scary, nothing dangerous is actually happening to her.
Remind her that anxiety symptoms are the result of her body telling her, "there's danger, you need to respond to it!" The trouble is that the danger is not something she needs to physically fight or run away from (fight or flight response) but is more emotional and cognitive danger. Maybe you can talk to her about what it's like to transition from homeschool to HS.
Brainstorm with her about what might make it feel safer to go to the school until you can get some help, such as shorter days, arrive earlier to adjust, possibly talk to her teacher (this is a good idea for some people but not for others).
I hope that helps a bit. Please write back and keep us posted.
Regards,
Jennifer Fee, Psy.D.
www.thestressmasters.com